The present invention relates to certain novel hydroquinone type compounds and their use as stabilizers for synthetic resins such as butadiene polymers.
In extrusion molding or injection molding of butadiene polymers such as solution-polymerized polybutadiene rubber (BR), solution-polymerized styrene-butadiene copolymer rubber (SBR), and styrene-butadiene block copolymer (SBS) or high-impact polystyrene modified with BR, SBR or SBS, high temperature and high speed processing is required. In such processing, fish eye gel often occurs due to insufficient thermal resistance, resulting in problems such as deterioration of film properties or discoloration. Solution of these problems has been desired.
It has been well known to use various antioxidants of phenol type, phosphorus type and sulfur type during preparation and processing of butadiene polymers. For example, phenolic antioxidants such as 2,6-di-t-butyl-4-methylphenol, 2,2'-methylenebis(6-t-butyl-4-methylphenol), n-octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, triethylene glycol bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate], pentaerythrityl 7 tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]and 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4 hydroxybenzyl)benzene are used alone or in combination with phosphorus type antioxidants such as tris(nonylphenyl) phosphite and distearyl pentaerythrityl diphosphite or in combination with sulfur type antioxidants such as dilauryl thiodipropionate, dimyristyl thiodipropionate, distearyl thiodipropionate and pentaerythrityl tetrakis(3-laurylthiopropionate).
However, these methods are not sufficient to prevent thermal deterioration (gelation) which may occur, especially in the absence of oxygen, at high temperature processing of butadiene polymers, although they are effective against thermal oxidative deterioration or discoloration due to thermal oxidation in practical use of the polymers.
Furthermore, U.S. Pat. No. 4,525,514 mentions that 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate is effective as a stabilizer for butadiene polymers. This stabilizer exhibits the effect to prevent thermal deterioration (gelation), especially in the absence of oxygen, at a high temperature process for separation of the polymer from a polymer solution in preparation of butadiene polymers or at high temperature processing of butadiene polymers, but it has become apparent that this stabilizer does not have sufficient effect against thermal oxidative deterioration or discoloration due to the thermal oxidation in practical use of the polymers.
Moreover, as an antioxidant for various synthetic resins for preventing discoloration caused by oxidative deterioration in the presence of oxygen, U.S. Pat. No. 4,365,032 has proposed a monoester compound of 2,2'-alkylidenebis(4,6-di-alkyl substituted phenol). This patent, however, makes no mention of preventing thermal deterioration (gelation) which may occur, especially in the absence of oxygen, at a high temperature process for separating the polymer from a polymer solution in production of butadiene polymers or at high temperature processing of butadiene polymers. Besides, the compounds specifically exemplified in the patent showed no sufficient effect to prevent thermal deterioration, especially in the absence of oxygen, at a high temperature process in the production of butadiene polymers or at high temperature processing of butadiene polymers.